Puffed fried pork skins have been a popular snack food for many years. These are prepared by cutting raw pork skins into pellets, rendering the pellets and deep-fat frying the pellets at high temperatures until the pellets are puffed. The process suffers from several problems. It produces substantial quantities of small pieces of rendered pellets (called fines, balls and tails) which cannot be puffed into acceptable products and is therefore wasteful of the starting material. The rendering step is time-consuming, which substantially increases the cost of the product. The pellets, and correspondingly puffed product are the varying sizes and shapes, due to the difficulty in accurately cutting the rubbery raw (green) pork skins. This causes substantial difficulty in packaging the product in conventional film packages both in terms of processing and avoiding underweight packages. Further, since the varying sizes and shapes are puffed at the same temperature and for the same time (for practical manufacturing process), some of the odd sizes and shapes may incompletely puff and produce hard centers.
The art has sought to obviate one or more of these problems. For example, U.S. Pat. No. 2,547,747 proposes to use bacon rinds instead of green skins. The use of rinds, apparently, in the process avoids a separate rending step. The rinds are steam-cooked, ground, extruded into strips, cut in appropriate sizes and deep-fat fried or baked.
Somewhat similarly, U.S. Pat. No. 2,562,850 suggests that a high pressure steam cooking be carried out until bacon rinds are gelatinized. Thereafter, the gelatinized rinds are pressed to remove remaining fat, formed into sheets, cut, and deep-fat fried or baked.
In U.S. Pat. No. 2,947,635, the toughness often associated with some puffed pork skins is attributed to inadequate moisture removal in the frying step which results in the collapse of puffed cells in the fried skin. To avoid this difficulty, it is proposed that the frying include a differential pressure condition, e.g., the frying step is carried out in deep fat maintained in a vacuum system.
On the other hand, U.S. Pat. No. 2,907,660 teaches that the texture difficulties are due to varying moisture contents of the pork skins (including bacon rinds and green skins). The patent suggests heating the skins in hot oil until all visible vapor is removed and then further heating the skins in that oil under pressurized conditions of up to 20 psi. That intermediate product is said to be uniform in moisture content and will produce uniform puffed skins.
In U.S. Pat. No. 3,401,045, a process is described where raw (green) skins are cut and rendered in fat at higher temperatures for extended periods of time, i.e., until the green skins are cooked and are reduced in size to about one-half of the original size. These relatively hard, dry and tough pieces are then soaked in an aqueous flavoring solution, dried to a prescribed moisture content and puffed by deepfat frying.
A similar idea is stated in U.S. Pat. No. 3,428,462, which proposes low-rendering temperatures for initially cooking green skins, with increasing temperatures and the repeated addition of water to the heated fat vessel (the temperature of which must be very low) until the green skins are fully cooked. The cooked skins are puffed at higher temperatures in the latter portions of the process. This is said to supply the necessary moisture for the skins and avoid the difficulty of hard and impalatable product.
In copending application Ser. No. 734,967, filed on Oct. 22, 1976 and now U.S. Pat. No. 4,119,742, there is disclosed a process wherein certain of the above-noted problems are obviated in that the process uses a starting material which is particles of animal parts which are sufficiently high in collagen content to cause gelatinization thereof and at least 50% by weight thereof are rendered parts. In a particular form of the process, the "balls, tails and fines" (identified above) are used as the starting material. These particles are moisturized and gelatinized in a screw-type extruder having thermally controlled barrel sections to produce an extrudate which is smooth, glossy, and does not exhibit reversion characteristics (will not revert to an agglomeration of particulate material at room temperature). That extrudate is cooled, cut, dried, and deep-fat fried to produce a puffed product which closely resembles a conventional fried pork skin in taste, appearance, texture and mouth-feel. This process provides a substantial advance in the art, particularly in that the sizes and shapes of the extruded and cut material are substantially uniform and a uniform puffing can be achieved. This avoids difficulties in packaging and in regard to hard centers of the packaged product. Additionally, it recovers the otherwise waste "balls, tails, and fines" which accumulate in the rendering tanks.
The process of that copending application, however, does require rendered starting material (at least 50% of the animal parts must be rendered) and, thus, does suffer from the disadvantage noted above in connection with the rendering step. Accordingly, it would be of distinct advantage in the art if the rendering step, conventionally practiced in the art, could be avoided, while on the other hand achieving the advantages of the process described in the said copending application.